Slip agent for protecting glass

ABSTRACT

This disclosure features use of a paper or polymer film that includes a slip agent that can transfer to its surfaces. Once the paper or film is pressed against a glass sheet, this will leave a thin surface roughness of slip agent that can prevent or reduce glass surface scratches from other surfaces or particles during shipping or finishing (e.g., cutting to size, conveyance of glass), thereby improving the yield of glass shipments between glass forming plants and customers. The thin discontinuous layer of slip agent remaining on the glass surface can be washed off easily in subsequent washing processes. The paper or film can have the slip agent imbibed within the paper or coated on it as a surface member.

TECHNICAL FIELD

The field is slip agents for protecting glass sheets from scratching.

TECHNICAL BACKGROUND

The shipment of display glass has employed surface protection of bothsubstrate sides using a combination of laminated films with paperinterleaf or more recently, a very clean single layer paper-onlyinterleaf material. Referring to FIG. 1 (Prior art) in the formerprocess, three sheets were used between adjacent glass sheets 10, 12 and12, 14. Two outer layers of polymer film 16, 18 were coated onto facingsurfaces 20, 22 of the glass, which sandwiched a sheet of paper 24between them. The laminated film protection method requires a polymerfilm coater, films and a film peeler. This three layer interleaf addsextra process steps and sheets of material and increases manufacturingcosts. It is highly desirable to use a single layer interleaf materialto pack glass sheets at the bottom of the draw (BOD) in a fusion drawprocess, and to pack finished goods.

At the bottom of the draw the glass is unfinished and has sharp edgesthat chip easily during subsequent handling and finishing operations.This leads to an increased level of glass chips and other particles onthe glass that can cause scratching of the glass during subsequenthandling, finishing and shipping of the glass. The surface of the glassmay also be scratched by the handling and finishing equipment itself, orby dirt and glass particles on or from the handling and finishingequipment and from other sources. It is desirable to protect the surfaceof the glass from scratching during handling, finishing and shippingoperations downstream of the BOD.

TECHNICAL SUMMARY

In general, a method of protecting glass sheets from scratchingcomprises applying slip agent to a surface of a glass sheet beforefinishing and/or shipping operations. The slip agent can be present onthe glass sheet in an amount ranging from 1 to 10,000 nanograms percentimeter². Scratching of the glass sheet is inhibited during thefinishing and/or shipping operations using the slip agent. The slipagent can be formed as a discontinuous layer on the glass sheet.Application of the slip agent to the surface of the glass sheet can formsurface roughness on the glass sheet comprising the slip agent. Part ofthe slip agent can be transferred onto particles present on the glasssheet, thereby protecting the surface of the glass sheet fromscratching. Alternatively rolling or sliding of particles on the slipagent, rather than directly on the glass sheet, can prevent scratchingof the glass sheet. The glass surface is cleaned to remove the slipagent and any particles on the glass sheet. The slip agent may beapplied to the glass by any means, such as transfer using paper or film,spraying or dipping. Spraying or dipping may apply a thicker coating ofslip agent on the glass sheet than transfer using paper or film.

Another aspect of this disclosure is a method of protecting glass sheetsfrom scratching comprising applying a slip agent to a surface of a glasssheet before a finishing operation. The slip agent may form adiscontinuous layer on the glass. The glass sheet has no lamination ofslip agent containing material on it (e.g., no Visqueen film islaminated onto the glass during finishing). The slip agent comprises along chain fatty ester or long chain fatty amide. Scratching of theglass sheet during the finishing and handling operations is inhibitedusing the discontinuous layer of slip agent.

Modification of an interleaf paper or polymer film with slip agent,followed by transfer of slip agent to the surface of glass sheetsstacked in a temporary shipment package with the modified interleafpaper or polymer film between each glass sheet, provides the surface ofthe glass with a thin layer of slip agent that protects the glasssurfaces from scratches during crate packing, in-plant handling andprocessing directly on horizontal finishing lines after the paper isremoved for finishing. The slip agent transferred to the glass preventsscratches on a glass surface from bottom of the draw (BOD) to finishing(e.g. during shipment between glass forming plants), currently a problemfor large sized (generation 8 and 10) glass, as well as shipment andhandling to customers of the glass manufacturer. It is believed that theslip agent on the glass forms a micro surface roughness formingdiscontinuous layer on the surface of the glass. This disclosure refersto paper or film that is applied to the glass sheet for transfer of theslip agent to the glass sheet, and to interleaf paper or film that isdisposed between sheets of glass, which may or may not transfer the slipagent to the glass sheet.

This disclosure features use of a carrier membrane, for example, a paperor polymer film that includes a slip agent that can transfer to thesurface of the glass. Once the paper or film is pressed against theglass sheet, this will leave slip agent on the surface of the glass thatcan prevent or reduce glass surface scratches from other surfaces orparticles during finishing (e.g., edge grinding), handling and shippingoperations, thereby improving the yield of glass during finishing aswell as during shipment between glass forming plants and customers. Theslip agent remaining on the glass surface can be washed off easily insubsequent washing processes. The paper or film can have the slip agentimbibed within the paper or coated on it as a surface coating. Althoughthe term “imbibe” is used to generally describe the presence of slipagent in the paper as by submerging in slip agent liquid, and “coating”for application of slip agent to the outside of the paper, the terms maybe used interchangeably in this disclosure.

The specific slip agent can be a long chain fatty ester or a long chainfatty amide, for example, erucamide. The slip agent composition imbibedwithin or coated on the paper may include any other chemical agent thatcan be incorporated into paper to prevent scratches from inorganicparticles while leaving residuals on the glass surfaces that alsoprevent scratching when present in very small amounts. The slip agentresiduals are easily removed using standard glass washing processes andequipment

This disclosure features methods of applying a slip agent onto thesurface of a glass sheet, and the glass sheet itself that contains thisslip agent on its surface. Various techniques can be used to apply theslip agent to the glass, such as compressing interleaf paper or polymerfilm containing the slip agent between adjacent glass sheets in a stackof glass sheets. Another technique to apply the slip agent to the glasssheet is to compress a paper or polymer film including the slip agentbetween pressure rollers and the glass on one or both sides of a glasssheet. Yet another way to apply the slip agent to the glass sheet is tolaminate a slip agent containing polymer film to the glass sheet (e.g.,Visqueen film) and then to strip the laminated film from the glass sheetbefore the finishing process. When the slip agent is applied to theglass sheets using the pressure roll process, laminated film process, orstacked glass with interleaf compression process, a first form ofscratch protection to the glass sheets is provided. The slip agent thatremains on the glass sheets offers the glass sheet first scratchprotection along the finishing line where the glass sheet undergoes edgegrinding and washing operations. When the slip agent imbibed or coatedinterleaf paper or polymer film is inserted between glass sheets in astack, the slip agent offers a second form of protection againstscratches from particles present between the glass sheets of the stack.The terms, first form of scratch protection and second form of scratchprotection, are arbitrary terms used to differentiate between (a)preventing scratching of glass sheets in a stack using interleaf paperor film that is coated or imbibed with slip agent (second scratchprotection) from (b) preventing scratching by leaving a slip agent onthe glass surface, such as by transfer of slip agent from the paper orfilm and removal of the paper or film from the glass surface (firstscratch protection).

In general, the method of protecting glass sheets from scratching cancomprise positioning slip agent containing paper or polymer film on oneof the glass sheets. The slip agent can be a long chain fatty ester orlong chain fatty amide slip agent. The slip agent is present on at leastthe surface of the paper or film in contact with the glass sheet. Thepaper or film is pressed against or between the glass sheets and a smallportion of the slip agent on the paper or film is transferred onto theglass sheets. The paper or film is then removed from the glass sheet,leaving the transferred slip agent on the glass providing the firstscratch protection. The transfer of a portion of the slip agent onto theglass sheet can form surface roughness on the glass sheet comprising theslip agent. The first scratch protection provides protection againstscratches during subsequent finishing and handling operations, such asalong the finishing line, where scratching may be caused by rolls orrollers, steel cut tables, steel bars of glass separation devicesassociated with the cut tables, and other equipment. This scratching isresisted by moving particles (e.g., glass and other particles) againstthe slip agent rather than directly against the bare glass. The secondscratch protection is provided when the paper or film is insertedbetween glass sheets within a stack, whereby scratching from glassparticles or other particles is resisted by moving the particles againstthe slip agent on the paper rather than against the bare glass.

In applying the slip agent to the glass sheet via compression in a stackof glass, an additional glass sheet is placed against the paper (nowreferred to as interleaf paper as it is sandwiched between adjacentglass sheets) such that the slip agent is presented from the interleafpaper in contact with the additional glass sheet. The steps ofpositioning the interleaf paper against a glass sheet and applyinganother glass sheet on top of the interleaf paper are repeated until astack of glass sheets is arranged with a sheet of interleaf paperbetween each pair of adjacent glass sheets. The steps of pressing theinterleaf paper against the glass sheet and transferring the slip agentto the glass sheet occur when the interleaf paper located between theglass sheets is compressed as a result of a weight of the glass sheetsin the stack. In the second form of scratch protection, scratching fromglass or other particles between the glass sheets is resisted by moving(rolling or sliding) the particles against the slip agent on theinterleaf paper while the interleaf paper is within the stack, ratherthan moving the particles on the glass. Alternatively, scratching may beprevented by keeping particles on the glass stationary and rolling orsliding the slip agent on the glass and particles. The first scratchprotection can be achieved by slip agent that remains on the surface ofthe glass after separating the glass sheets of the stack and removingthe interleaf paper. Therefore, the compression technique of applyingslip agent to the glass sheet provides both the first and second formsof scratch protection.

Regarding details of the method, the interleaf paper or polymer film cancomprise one interleaf sheet including slip agent protruding from (e.g.imbibed in or coated on) both sides of the interleaf sheet.Alternatively, the interleaf paper or film can comprise two interleafsheets, each imbibed or coated on only one side with the slip agent andarranged such that the slip agent faces outwardly away from the otherinterleaf sheet. Now, scratching is avoided (second scratch protection)by the slip agent contacting the particles between the interleaf paperor film and the glass. Also, a portion of the slip agent is transferredto the glass sheet (first scratch protection). In both cases, scratchingof the glass sheet is minimized by the slip agent.

Regarding further details of the method, the interleaf paper can besubjected to a super calendar operation, or not. The paper or film cancomprise erucamide as the long chain fatty amide and an alkyl or alkenylketene sizing agent. The slip agent can be present on the glass sheet inan amount ranging from 1 to 10,000 nanograms per centimeter, moreparticularly, in an amount ranging from 1 to 3000 nanograms percentimeter², even more specifically, in an amount ranging from 1 to 500nanograms per centimeter².

In a process of applying the slip agent from slip agent imbibed orcoated paper or polymer film using rolls, the method includes providingon one or both sides of a glass sheet the paper or polymer film wound ona feed roll, with the paper or film extending from the feed roll to atake-up roll. Next, as the paper or film advances from the feed rollonto the take-up roll, the paper or film and the glass sheet arecompressed between rollers on either side of the glass sheets, therebypressing the paper or film against the surface of the glass sheet andtransferring a portion of the slip agent to the surface of the glass.The paper or film is removed from contact with the glass sheet once theglass sheet passes through the rollers traveling to the take-up roll.

In another process of applying the slip agent to the glass sheet, a slipagent containing polymer film is applied as a laminate on the glasssheet and then the laminate film is stripped from the glass sheet toresult in the transfer of slip agent to the glass sheet.

Another embodiment of this disclosure is a sheet of glass itself. Theglass sheet comprises a slip agent distributed across a major surface ofthe glass by any means. The slip agent comprises a long chain fattyester or a long chain fatty amide. The slip agent is distributed on theglass sheet in an amount ranging from 1 to 10,000 nanograms percentimeter², more particularly, in an amount ranging from 1 to 3000nanograms per centimeter², even more specifically, in an amount rangingfrom 1 to 500 nanograms per centimeter². The slip agent can be formed asa discontinuous layer on the glass sheet. The slip agent can bediscontinuously distributed across the major surface(s) of the glasssheet as a surface roughness comprising the slip agent. The long chainfatty amide can comprise erucamide. Compounded into the paper or polymerfilm material, the slip agent acts as an internal lubricant thattransfers to the surface where it is presented against the glass. Inthis disclosure, the lubrication is provided to surfaces of glass sheetonto which the slip agent is applied or otherwise transferred by thepaper or polymer film material or by other means.

On the other hand, the interleaf paper or film can comprise twointerleaf sheets, each coated or imbibed on only one side with the slipagent and arranged such that the slip agent coated side faces inwardlytoward the other interleaf sheet. This enables the adjacent glass sheetsof the stack to slip relative to each other as the slip agent of the twointerleaf sheets between the adjacent glass sheets slide relative toeach other, but the uncoated surfaces of the interleaf sheets do notslide relative to the glass sheets, thereby achieving the second scratchprotection. In this case, the particles between the interleaf sheets andthe glass do not move upon movement of the sheets, but rather movementoccurs between the adjacent interleaf sheets away from the glasssurfaces. However, when using this inwardly facing, single-side coatedinterleaf paper or film, slip agent would need to be separately appliedto the glass sheets in order to achieve the first scratch protection,because the facing interleaf sheets would not transfer any slip agent tothe glass sheets. When the slip agent coated or imbibed sides of theinterleaf sheets face each other, this can be used for transfer betweenglass forming plants and temporary storage of glass within the sameplant, not for use on the finishing line.

Prevention of scratches during handling and shipment using the slipagent at the surface of the interleaf provides the following advantages.It will yield improvement through scratch reduction. There will be acost reduction through process simplification and film coatingelimination. Scratching can be avoided using the paper or film at thebottom of the draw on difficult to protect unfinished glass havingparticle chips from unground edges and other sources. It is aninexpensive approach versus other alternatives. No additional surfacewashing techniques are needed to make the glass surface less active andremove particles that could scratch in subsequent washing and handling.

Many additional features, advantages and a fuller understanding of theinvention will be had from the accompanying drawings and the detaileddescription that follows. It should be understood that the aboveTechnical Summary provides a description in broad terms while thefollowing Detailed Description provides a more narrow description andpresents embodiments that should not be construed as necessarylimitations of the broad invention as defined in the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a view showing the prior art use of Visqueen film laminationon glass with a sheet of paper between the film (a three layer system);

FIG. 2 is a view of a single interleaf paper or film between glasssheets;

FIG. 3 is a view showing use of a double sided coated interleaf paper orfilm before application to the glass sheets;

FIG. 4 shows a compressed stack of glass sheets and second scratchprotection provided by the slip agent between the interleaf and theglass sheet;

FIG. 5 shows separated glass sheets and first scratch protectionprovided on the glass sheets in the form of a slip agent surfaceroughness discontinuous layer;

FIG. 6 is a view showing use of single side coated interleaf paper orfilm before application to the glass sheets in which one slip agentcoating faces away from the coating of the other interleaf;

FIG. 7 shows a compressed stack of glass sheets and second scratchprotection provided by the slip agent between each interleaf and theglass sheet;

FIG. 8 shows separated glass sheets and first scratch protectionprovided on the glass sheets in the form of a slip agent surfaceroughness discontinuous layer;

FIG. 9 is a view showing use of single side coated interleaf paper orfilm before application to the glass sheets in which one slip agentcoating faces toward the coating of the other interleaf;

FIG. 10 shows a compressed stack of glass sheets and slippage betweenthe interleaf sheets providing scratch protection;

FIG. 11 shows the separated glass sheets and no slip agent surfaceroughness protection provided on the glass sheets;

FIG. 12 shows a method of applying a slip agent surface roughnessdiscontinuous layer to a glass sheet using rollers;

FIG. 13 compares the defects and yields of glass sheets subjected to aVisqueen peeled film, untreated paper, erucamide coated paper, andsingle layer polymer film;

FIG. 14 shows the contact angle on glass treated with a Visqueen peeledfilm, untreated paper, erucamide and stearamide imbibed paper underdifferent papermaking conditions, and single layer polymer film; and

FIG. 15 shows the effect of temperature on the contact angle on glasstreated with erucamide imbibed paper and single layer polymer film.

DETAILED DESCRIPTION

Referring to FIG. 2, a slip agent can be applied to a glass sheet in onetechnique through compression when preparing a stack of glass sheets forshipment (hereinafter to be referred to as the “compression method”). Asillustrated, a carrier membrane, for example, a single sheet of theinterleaf paper or polymer film containing slip agent 26 is positionedbetween adjacent glass sheets 28, 30 and 30, 32 in a stack 34 of glasssheets (FIG. 4). A stack of glass sheets can include 100 or more sheets,for example. Referring to FIG. 3, slip agent protrudes from both sides37, 39 of interleaf sheet 40 facing opposing surfaces 42, 44 of theglass sheets. When the interleaf sheet(s) 40 are compressed between theglass sheets 28, 30 due to the weight of the glass sheets in the stack(FIG. 4), a small portion of the slip agent is transferred to thesurfaces 42, 44 of the glass. Upon unstacking of the glass sheets 28, 30and separation of the interleaf paper or film from the glass sheets, thetransferred portion of the slip agent remains on the glass sheets (FIG.5) providing the first scratch protection for the glass. When the glasssheets are stacked with the interleaf sheet(s) 40 between the glasssheets 28, 30, the slip agent provides the second scratch protection forthe glass sheets against any particles 46 located between the glasssheets during handling and storage of the stack of glass sheets.

Although the mechanics of the first and second scratch protection arenot fully understood, it is believed particles such as glass chips mayroll or slide upon the slip agent rather than on the bare glass, therebypreventing scratches on the glass. The slip agent may roll between theglass sheet and the interleaf paper or film, or it may coat particlesthat roll between the interleaf paper or film, or both.

While the slip agent protruding from the interleaf sheet or film andtransferred onto the glass sheet is depicted in the figures, it will beappreciated that the slip agent, interleaf, and glass sheets are not toscale. Only nanogram amounts per centimeter² of the slip agent istransferred to the glass sheet. The slip agent may not actually resemblewhat is shown in the drawings. The slip agent molecules may be polar,which could help to align the molecules on the interleaf paper and film,and on the glass sheet. This may produce a glass sheet with surfaceroughness on one or both sides thereof. Interior glass sheets of thestack may include a discontinuous layer of slip agent that forms surfaceroughness layer on both sides of the glass sheet.

Another approach is to use the compression method to apply the slipagent when coated on only one side of an interleaf sheet. Two suchsingle-sided interleaf sheets 50, 52 would be used. The interleaf sheets50, 52 can be placed between two glass sheets with their slip agentcoated sides facing outwardly away from each other, as shown in FIG. 6.Upon compression of the interleaf sheets between the two glass sheets28, 30 due to the weight of the stack of glass sheets (FIG. 7), aportion of the slip agent is transferred to the glass sheets surfaces58, 60 and provides second scratch protection. While the glass isstacked with interleaf sheets as shown in FIG. 7, particles such asglass chips 46 between the glass sheets can roll or slide on the slipagent 36 on the interleaf sheets 50, 52 instead of on the bare glasssurfaces 58, 60, or the particle movement could be inhibited by the slipagent contact between the paper or film sheet and the glass sheet. Thefacing surfaces 64, 66 of the interleaf sheets may provide some slip inthe stack, but the primary slip would be along the plane between theslip agent coated interleaf surfaces 54, 56 and the glass surfaces 58,60. A portion of the slip agent is then transferred onto the inwardlyopposing surfaces 58, 60 of adjacent glass sheets as shown in FIG. 8,providing the first scratch protection for the glass in which theparticles roll or slide on the slip agent 48 remaining on the glassafter the interleaf sheets 50, 52 have been removed from the glasssheets.

The compression method for applying the slip agent to the glass sheetsvia interleaf sheets placed between the sheets of glass in a stack ofglass sheets offers second scratch protection to the glass sheets withinthe stack. That is, any glass particles from the cut edge (or otherparticles) that are located between the glass sheets will move againstthe slip agent on the interleaf sheets rather than against the bareglass, which prevents scratching of the glass when the glass sheets ofthe stack move relative each other. On the other hand, slip agent may belocated between the glass sheet and the particles. Moreover, once theglass sheets of the stack are separated, the interleaf sheets areremoved and the glass sheets are ready to be placed on the finishingline; the glass sheets contain the slip agent (first scratchprotection). At this point, no interleaf sheets remain on the glasssheets during the finishing run. The glass sheets are solely protectedby the slip agent on the surface of the glass. The interleaf paper thatperformed better than others as described in the examples below is onewhich was imbibed with or coated with erucamide as the long chain fattyamide as well as a sizing agent such as alkyl ketene dimer.

Another technique for applying slip agent to glass sheets disclosedherein is coating (laminating) a polymer film containing the slip agentto the glass sheet (e.g., Visqueen polymer film that includes erucamideslip agent) and then stripping the film from the glass sheet. After thefilm is stripped from the glass, some of the slip agent remains on theglass sheet. This provides the first form of scratch protection of theglass along the finishing line after the film has been removed.

In a process of applying the slip agent from the paper or polymer filmto the glass sheets using rolls, the method includes providing on bothsides of a glass sheet the paper or polymer film 80 wound on a feed roll84, the paper or film extending from the feed roll to a take-up roll 82.Next, as the paper or film 80 advances onto the take-up rolls, the paperor film and the glass sheet 86 are compressed between rollers 88 oneither side of the glass sheet (in a direction shown by arrows 90). Theglass sheet moves in a direction 92. The glass sheet may also move inthe opposite direction, opposite to the traveling direction of the paperor film. This presses the slip agent 36 protruding from the paper orfilm 80 onto the glass sheet 86 and transfers some slip agent 36 fromthe paper or film onto the glass sheet. The paper or polymer film isremoved from the glass sheet once the sheet passes through the rollersand then it travels to the take-up roll where it is wound up. The paperor film may still contain a sufficient quantity of slip agent aftercontacting the glass sheet for enabling reuse of the paper or film toapply slip agent to additional glass sheets or it might only be used onetime.

Two single-sided interleaf sheets 68, 70 between adjacent glass sheetsin a stack of glass sheets, wherein the coated sides 72, 74 of twointerleaf sheets are inwardly facing relative to each other (FIG. 9),may be employed to achieve the second scratch protection only for theglass sheets. The interleaf sheets have outer surfaces 76, 78 withoutslip agent facing the inner surfaces 58, 60 of the adjacent glasssheets. In this way, the friction where the two interleaf sheets'uncoated sides contact the sheets of glass is greater than the frictionwhere the two interleaf sheets' coated sides contact each other. Uponcompression of the interleaf sheets between the glass sheets as shown inFIG. 10 any particles 46 on the bare glass are prevented from scratchingthe glass because the principal movement between adjacent glass sheetsis via slip agent 36 along the plane between the interleaf sheetsurfaces 72, 74 (e.g. where friction is the lowest), thereby providingthe second scratch protection of the glass. Once the glass sheets areseparated no slip agent transfers to the opposing surfaces 58, 60 of theglass sheets (FIG. 11). If first scratch protection of the glass isdesired for the finishing line after the interleaf sheets have beenremoved from the glass, then the slip agent would need to be applied tothe surface of the glass sheets through another means.

The paper used in this disclosure is made using a Fourdrinier papermaking machine and can be purchased from the Thilmany Pulp & PaperCompany. An overview of a Fourdrinier machine is described in U.S. Pat.No. 7,189,308, which is incorporated herein by reference. The optionalalkyl ketene dimer sizing agent is added at the wet end of the process.In addition, the slip agent can be added at the size press such aspassing the paper through a bath including the sizing agent. Then, thepaper passes through drier cans at a temperature exceeding a meltingpoint of the erucamide. Next, at the dampener where water is added toobtain a proper curl of the paper, this is another location at which theslip agent can alternatively be added. At the dampener the slip agentcan be coated onto one side of the paper. Then, the paper passes to thesupercalendar, which squeezes the paper between opposing denim coveredstainless steel rolls and stainless steel rolls. At this location fibersare locked down in the paper. The paper of this disclosure can becalendared or uncalendared. Then the paper travels to a rewinder. Theslip agent can alternatively be coated onto the paper by spraying at thesupercalendar or the rewinder. Suitable paper is described inpublication WO 2008/002584, which is incorporated herein by reference.

The slip agent can be added to the paper as a dispersion (e.g., a waxdispersion) or an emulsion. The slip agent may be added as a solid tothe polymer resin that forms the polymer film. Stable aqueous waxdispersions are disclosed in U.S. Pat. Nos. 5,743,949 and 4,481,038,which are incorporated herein by reference in their entireties. Thesupplier of the emulsion can also provide defoamer and surfactant in theslip agent emulsion or dispersion to facilitate application of the slipagent to the paper. A suitable defoamer is ethylene his distearamide.

Compounds that might be suitable as slip agents include at least onelong chain fatty acid ester or fatty acid amide. The long chain fattyacid esters and fatty acid amides of this disclosure are derivatives ofsaturated and unsaturated normal fatty acids ranging from fourteen tothirty-six carbon atoms. Representative fatty acids are, for example,tetradecanoic, pentadecanoic, hexadecanoic, heptadecanoic, octadecanoic,nonadecanoic, eicosanoic, hencosanoic, decosanoic, tetracosanoic,pentacosanoic, tricosanoic, hexacosanoic, triacontanoic,dotriacontanoic, tetratriacontanoic, hentriacontanoic,pentatriacontanoic, hexatriacontanoic acids, myristic, palmitic,stearic, arachidic, behenic and hexatrieisocontanoic (C₃₆) acids, oleic,palmitoleic, linolenic and cetoleic, and the like.

Long chain fatty amides are preferred as slip agents, suitable slipagent might include one or more of the following: unsaturated fatty acidmonoamide (e.g., oleamide, erucamide, recinoleamide); saturated fattyacid monoamide (preferably, lauramide, palmitamide, arachidamide,behenamide, stearamide, 12 hydroxy stearamide); N-substituted fatty acidamide (e.g., N-stearyl stearamide, N-behenyl behenamide, N-stearylbehenamide, N-behenyl stearamide, N-oleyl oleamide, N-oleyl stearamide,N-stearyl oleamide, N-stearyl erucamide, erucyl erucamide, erucylstearamide, stearyl erucamide, N-oleyl palmitamide); methylol amide(e.g., methylol stearamide, methylol behenamide); unsaturated fatty acidbis-amide (e.g., ethylene bis-oleamide, hexamethylene bis-oleamide,N,N′-dioleyl adipamide, ethylene bis oleamide, N,N′-dioleyl sebacamide);saturated or unsaturated fatty acid tetra amide; and saturated fattyacid bis-amide (e.g., methylene bis-stearamide, ethylene bis-stearamide,ethylene bis-isostearamide, ethylene bis-hydroxystearamide, ethylene bisstearamide, ethylene bis-behenamide, hexamethylene bis-stearamide,hexamethylene bis-behenamide, hexamethylene bis-hydroxystearamide,N,N′-distearyl adipamide, N,N′-distearyl sebacamide).

Specific long chain fatty amides that may be suitable are erucamide,stearamide, oleamide and behenamide. Fatty amides are commerciallyavailable from Humko Chemical Company and include, for example KemamideS (stearamide), Kemamide U (oleamide), Kemamide E (erucamide). Inaddition, fatty amides are commercially available from Croda UniversalLtd., and include, for example, Crodamide OR (oleamide), Crodamide ER(erucamide), Crodamide SR (stereamide), Crodamide BR (behenamide).

The sizing agent used herein is known as an alkyl ketene dimer (AKD);these types of sizing agents are described in U.S. Pat. No. 6,576,049,which is incorporated herein by reference in its entirety. Specificexamples of AKD sizing agents that may be suitable in the presentinvention include but are not limited to octyl ketene dimer, dodecylketene dimer, tetradecyl ketene dimer, decyl ketene dimer, hexadecylketene dimer, eicosyl ketene dimer, docosyl ketene dimer, octadecylketene dimer, tetracosyl ketene dimer. Also included are those preparedfrom organic acids and mixtures of fatty acids such as those found inpalmitoleic acid, rincinoleic acid, oleic acid, linoleic acid, linolenicacid, olive oil, coconut oil, palm oil, and peanut oil. Mixtures of anyof such acids may also be used. AKD sizing agents can include but arenot limited to those comprising at least one alkyl group comprising fromabout 8 to about 36 carbon atoms.

The slip agent can be washed off the glass at the finishing line usingknown washing processes and equipment, including brushes, ultrasound,water jet spraying, and detergent (e.g., potassium hydroxide detergent)at a pH of 10-12. The washing fluids will not dissolve the erucamidesurface roughness, but it is nevertheless removed from the glass sheetsby the mechanical action cleaning processes and devices of the finishingline.

This disclosure will now provide a description by way of the followingexamples, which are for the purpose of illustration and should not beinterpreted to limit the invention as defined in the claims.

Example 1

The following conditions were evaluated: 2-sided erucamide imbibed paperin which the erucamide was applied at the size press (Condition 1);1-sided erucamide imbibed paper in which the erucamide was applied atthe size press (Condition 2); 2-sided erucamide imbibed paper in whichthe erucamide was applied at the size press, the paper including alkylketene dimer (AKD) (Condition 4); 2-sided stearamide imbibed paper inwhich the stearamide was applied at the size press, the paper includingAKD (Condition 6); erucamide coated paper in which the erucamide wasapplied at the dampener (Condition 7); and stearamide coated paper inwhich the stearamide was applied at the dampener (Condition 8). Thesupercalendaring conditions were as indicated in the following Table 1.The number of nips in the supercalendar conditions refer to the numberof rollers through which the paper passed and these rollers were eitherheated or cold as indicated. The erucamide and stearamide were appliedto the paper as aqueous dispersions, wherein the 10% value indicates theconcentration of the erucamide or stearamide in the dispersions.

TABLE 1 Roll Roll Roll Coating Condition Supercalender Lot Serial WidthWeight Length # Conditions Conditions Number (Gen) (kg) (m) 8 stearamide(10%) @ 5 nip cold stack N2423275 lab size dampener N2423276 Gen 5 3113,658 N2423608 Gen 8 468 2,713 7 erucamide (10%) @ 6 nip cold stackN2423279 lab size dampener N2423280 Gen 5 172 1,981 N2423281 Gen 8 3111,829 1 coated 2 side (C2S) full hot stack N2423266 lab size erucamide(10%) @ size N2423265 Gen 5 336 3,975 press N2423252 Gen 8 476 2,900non-supercalendered N2423269 lab size N2423268 Gen 5 325 3,975 N2423256Gen 8 462 2,900 2 coated 1 side (C1S) full hot stack N2423261 lab sizeerucamide (10%) @ size N2423262 Gen 5 321 3,975 press N2423258 Gen 8 4682,900 4 coated 2 side erucamide 5 nip hot stack N2423272 lab size (10%)@ size press; with N2423271 Gen 5 180 2,134 internal AKD N2423610 Gen 8468 2,896 6 coated 2 side stearamide 5 nip hot stack N2423202 lab size(10%) @ size press; with N2423283 Gen 8 251 1,554 internal AKD 6 coated2 side stearamide non-supercalendered N2423255 lab size (10%) @ sizepress; with N2423254 Gen 8 288 1,783 internal AKD

The initial testing of the papers from the paper mill includedcoefficient of friction testing as shown below.

TABLE 2 Coefficient of Friction of Papers Sheet Sheffield COF to steelCOF Condition Side Smoothness Test # 1 Test # 2 average WR- Control felt327 0.27 0.31 0.29 139 wire 347 0.29 0.31 0.30 1 2 sided Eruc felt 1270.25 0.27 0.26 SC wire 152 0.29 0.29 0.29 1b 2 sided Eruc felt 297 0.280.30 0.29 NC wire 321 0.27 0.23 0.25 2 1 sided Eruc felt 100 0.27 0.270.27 SC wire 115 0.24 0.29 0.27 2b One sided Eruc felt 332 0.23 0.300.27 NC wire 335 0.26 0.27 0.27 3b One sided Eruc felt 338 0.29 0.310.30 NC w/AKD wire 346 0.31 0.27 0.29 4 2 sided Eruc felt 96 0.29 0.270.28 w/AKD SC wire 122 0.29 0.22 0.26 4b 2 sided Eruc felt 344 0.25 0.230.24 w/AKD NC wire 352 0.28 0.27 0.28 6 2 sided Stear- felt 109 0.280.31 0.30 SC 5 nips wire 150 0.30 0.25 0.28 6b 2 sided felt 342 0.260.23 0.25 Stearamide wire 362 0.30 0.28 0.29 w/AKD NC 7 Eruc @ felt 1660.21 0.15 0.18 dampener SC wire 172 0.27 0.29 0.28 7b Eruc @ felt 3220.16 0.15 0.16 dampener NC wire 327 0.30 0.26 0.28 8 Stear @ felt 1430.26 0.27 0.27 dampener SC wire 158 0.24 0.26 0.25 8b Stearamide @ felt327 0.26 0.27 0.27 dampener NC wire 341 0.26 0.24 0.25 *b samples arenon-supercalendered

The coefficient of friction (COF) data support the understanding thatthe mechanism of action of the slip agent is not primarily by loweringthe coefficient of friction. In Table 2, COF to steel means rubbing asteel plate across the paper to ascertain the COF. The above data showsthat most papers have similar COF values. This includes un-coated paper.The only significantly lower COF results were obtained from the singlesided dampener trial results (e.g. the slip agent was applied to thepaper at the dampener), for both calendared and uncalendared papers.Therefore, COF alone is not responsible for the scratch protectiondifferences to be shown later in this disclosure, produced by Condition1 (2-sided erucamide imbibed paper in which the erucamide was applied atthe size press) using supercalendared paper. This was supported byearlier testing using solid slip agents on glass versus the liquid slipagent, glycerol, in which the solid slip agents outperformed the liquidslip agents. Here the solid particles were better in scratch prevention,although both provided low COF. In addition, the supercalendardifferences indicate that the calendared paper may not be driving theslip agent towards or away from the surfaces. Finally, from contactangle data discussed below, it was inferred that the dampener processresults in the most slip agent on the felt-side paper surfaces, and thatit does not migrate to the papers wire-side upon rolling.

Example 2 Testing of Coated Papers and Selection of 2-Sided ErucamideCoated Paper from the Supercalendar Process for Scale Up

The paper-conditions that were deemed acceptable from the mill trialwere Condition 1 (2-sided erucamide imbibed paper applied at the sizepress) and Condition 6 (2-sided stearamide imbibed paper applied at thesize press and including AKD), with calendared and uncalendared paperavailable from each. Other conditions became useful primarily for latertesting since there were line issues with foaming, coating pumping,coating concentration variations, and roll alignment during otherconditions. Although the dampener trials were satisfactory, the 1-sidedcoatings were not used for scale-up, since at this time two sheets ofcoated paper per substrate had a high cost. Best results were obtainedunder Condition 4 (2-sided erucamide imbibed paper in which theerucamide was applied at the size press, the paper including AKD).

Stain testing was conducted using washed glass (e.g., 2% Semiclean KGsolution at 45° C. for 15 minutes) having a low particle count, stackedfor 16 hours at 50° C. and 85% relative humidity under a packing weight(e.g., 4.4 kg). Particle density of the glass sheets was measured afterwashing using ETHAN (or MDM2) inspection system.

A scratch test was developed to evaluate motion of the materials rubbedacross the glass surface. As in stain testing, the glass sheets were 5×5inches. The glass was washed and had a low particle count. This testused a simple flat-bottomed container with the material attached to thebase to ride across the glass, not including glass chips, in arepeatable way. Loading, speed and number of passes can be controlled.Once the test was complete the results after washing were compared usinga particle density instrument.

4 materials at the top of Table 3 were evaluated to choose candidatesfor on-line tests. All results are listed in particles per squarecentimeter left on glass surfaces after testing. Results of 10 or lessfor stain are acceptable, while scratch numbers below 40 are generallyacceptable. All slip agents in Table 3 were applied at the size pressexcept the two noted for the dampener application. The tests showed thatstearamide had higher stain results compared to erucamide, which madeerucamide a more suitable slip agent.

TABLE 3 Scratch and Stain Data for New Single Layer Materials Month 1Month 2 Month 3 Scratch Scratch Scratch Coated Paper Condition StainAverage Median Stain Average Median Stain Average Median 2-SidedStearamide w/AKD, SC; C6 39.2 11.9 2-Sided Stearamide w/AKD, no SC; C6209 8.3 50.1 2-Sided Erucamide, SC; C1 5.7 25.7 2-Sided Erucamide, noSC; C1 1.7 22.4 Control, WR-139 Uncoated paper 2.4 1 4.4 34.1 16 1-sidedErucamide, size press; C2 4.1 3.5 2-sided Erucamide, w/AKD; C4 2.6 4.11-sided Erucamide, dampener; C7 9.6 30.9 1-sided Stearamide, dampener;C8 3.1 11.9 ENW53B (2%) SL polymer 4.1 10 ENW53B (1.5%) SL polymer 7.613.9

From Table 3, the best choices were from condition 1(C1), the 2-sidederucamide imbibed materials. Super-calendared (SC) and uncalendaredversions of C1 were evaluated further. All scratch analysis results(Table 3) are shown to be in an acceptable range.

Stearamide with AKD, condition 6 (C6) stained the glass more than theerucamide. Later data (Table 5) will show stearamide was in higherconcentration at the glass surface, before washing, compared toerucamide. The alkyl ketene dimer (AKD) used in C6 is a common sizingagent used in the paper industry. Addition of this less expensivematerial (AKD) was intended to bind to the paper interior and allow moreslip agent to migrate to or remain at the surface. For erucamide imbibedin the paper at the size press, Condition 4 (C4), there was a higheramount of material found on glass surfaces after contact with AKD versuswithout AKD.

The Month 3 result listed in Table 3 for condition C1 was high (50.1),as was the control result (16) since these samples were aged for 2 weeksat 50° C. in a humidity chamber with dense pack loading (23 g/cm²) and50% relative humidity. This temperature effect has been observed byseveral techniques to bring more erucamide slip agent to the papersurface.

Also shown are limited results for the polymer single layer (SL)interleaf. Those results were based on 3 replicates per test, due tosample availability. Usually stain is based on 15 replicates, andscratch on at least 5 replicates. The sample was a single layer polymerfilm (“SL polymer film”; i.e., no other separate independent layers)that included three sublayers, one being a central medium densitypolyethylene core. The core was made of a foam of medium densitypolyethylene. Two outer skin layers of low density polyethylenesandwiched the core. The total film thickness ranged from about 70 to120 microns.

Example 3 On Line Testing of 2-Sided Erucamide Coated Paper and SingleLayer Polymer Paper

Glass surfaces contacting one paper imbibed with erucamide (“Coatedpaper”) and one single layer polymer film imbibed with erucamide (“SLpolymer film”) were compared along with glass surfaces contactingun-coated paper and glass surfaces with Visqueen film residue afterpeeling (“Manually peeled Visqueen film”). Generation 8 lots of 100 foreach interleaf type were packed in separate crates then loaded onto thefinishing line. The order of run may be relevant. The Visqueen peeledsurfaces were run first while the uncoated paper was run second to befollowed by the Coated paper and SL polymer film test materials. TheVisqueen stripping left the most slip agent at the surface, while theuncoated paper left no slip agent protection. The expectation was thatslip agent residue from Visqueen deposited on machine parts would beremoved prior to testing the new materials by the glass packed inun-coated paper. Testing was carried out over two days with about a weekof separation between tests, due to line availability. Results arelisted in Table 4 below.

SIS is a known optical method for identifying defects in which defectsare measured by strobing light onto the glass and locating the defectsusing a scanning camera. IPC is a similar known optical defectmeasurement technique. Controllable yield was the number of glass sheetsthat included a critical defect that would have required scrapping orrecutting of the glass sheet divided by the total number of glass sheetstested.

TABLE 4 Input Controllable SIS Defect Sample Sheets Yield Counts IPC 1)Peeled 49 100% 150-190 Visqueen Film Uncoated 99 84% 1000-1400 PaperCoated Paper 100 97% 120-170 SL Polymer 30 90%  30-450 Film 2) Peeled 50100% 100-130 0.006 Visqueen Film Uncoated 100 67% 1000-1200 0.012 PaperSL Polymer 74 90% 120-180 0.017 Film

A useful representation of this data is shown in FIG. 13. This figureshows results from BOD through Finishing Testing of Materials. Note thatSIS defect counts while not including rejectable defects are a measureof surface cleanliness of the substrates, and therefore an indicator ofperformance beyond yield criteria. FIG. 13 shows that the lowest numberof defects and best yields were achieved using manually peeled Visqueenfilm (data labeled A), the Coated paper (data labeled C), and the SLpolymer film (data labeled D), whereas the worst yields were from theuncoated paper (data labeled B).

Example 4 Contact Angle Measurements

When the contact angle measured for a treated sheet of glass is higher,it means there is more of the treatment material on the glass. FIG. 14first shows the anticipated range of contact angles expected from thesurface of glass after peeling off Visqueen film, which includederucamide. The aged BOD surface is the contact angle that resulted frommany months of aging BOD sourced glass in a crate before peeling(indicated as Vpa in FIG. 14), while other contact angle data wasobtained by using washed glass with laminated Visqueen film which wasimmediately stripped (indicated as Vpf in FIG. 14). This table verifiesthat aging deposits more erucamide on the surface of the glass Vpa,raising the contact angle relative to the glass with the strippedlaminated Visqueen film Vpf. In FIG. 13 the 100% yields are observed forthe aged Visqueen film peeled surfaces. The next small bar P of FIG. 14represents the glass samples held overnight with only the dense packuncoated paper; this had almost no effect, and low contact angleindicates no transfer of coating material to the glass. The next set ofbars C1, C1unc, C2, C4, C6 and C6unc show the various conditions fromthe slip agent coated paper trials, with the unc in C1unc and C6uncindicating uncalendared paper, with the remaining bars being calendaredpaper. D1 and D2 were dampener trials of paper having 10% solids,erucamide loading. The last bar at the end Pf was for the single layerpolymer film run in FIG. 13. The higher contact angle of C1 versus thepolymer film concurs with the yield of 97% versus 90% observed in FIG.13.

All conditions were further lab-tested for stain and scratch as Table 1shows, and Condition C4, showed favorable results. Condition C4 withalkyl ketene dimer (AKD) showed a higher contact angle (FIG. 14) thanother conditions of coated paper. For this reason, the next trial usedpaper made by C4.

Example 5

The glass was placed in contact with the coated paper and held overnightin a clean room. This simulates the transfer of slip agent due tocompression of the glass sheets in a stack. The glass surfaces afterpaper contact were examined to confirm the transfer of slip betweenpaper and glass surfaces. Many analytical techniques were attempted butwere unable to determine this transfer due to the presence of very smallparticles of erucamide not uniformly spread on the surface of glass withlow coverage. The mass ESI (Electrospray ionization)-MS-MS, massspectrometry results did show both the identity and amount, using asolvent wash of the surface. Table 5 shows ESI MS-MS results for severaltrial paper coating conditions.

TABLE 5 Erucamide Transfer to Glass from Paper Stearamide Erucamide(ng/6.4 cm2) at (ng/6.4 cm2) Paper Type for Contact glass surface atglass surface Dampener, 10% solids, Stearamide 1120 Detected 5453Detected 2-Sided Stearamide w/AKD 1696 Detected Uncalendered 1303Detected 2-Sided Stearamide w/AKD 2206 Detected 2071 Detected 2-SidedErucamide w/AKD 262 163 1-Sided Erucamide  55 Visqueen, peeled 240 134Uncoated Paper Not Detected Not Detected Not Detected Not Detected

Each test was done in duplicate. Stearamide coatings were shown to becontaminated with erucamide, which shows that the stearimide sampleswere not pure. Erucamide with AKD showed transfer to the glass surfacein the range of peeled Visqueen film, with 1-sided Erucamide coatingtransferring less to glass, although the COF of the 1-sided (Table 2)was lower. The uncoated paper showed no slip agents. The high amounts ofstearamide transferred were not easily washed off the surfaces as shownin Table 3. The highest amount of stearamide transferred was without AKDbut at the dampener, where a higher surface concentration is likelysince the paper is near the end of the papermaking process, andcompletely formed, and denser versus at the size press.

Example 6

To enhance the amount of erucamide transferred from interleaf paper orpolymer film interleaf, the materials were tested at elevatedtemperatures. There were higher contact angles with increasedtemperatures for the two sided erucamide coated paper, Pc, but theeffect for the film, Pf, was much less significant than for the paper.There is a possibility that transfer of glass at higher than usualtemperatures in the shipment container with paper contact, ortemperature rises in warehouses could enhance the surface protection ofcoated papers. FIG. 15 shows this result. The base temperature of 19.4degrees C. was the clean room temperature.

Many modifications and variations of the invention will be apparent tothose of ordinary skill in the art in light of the foregoing disclosure.Therefore, it is to be understood that, within the scope of the appendedclaims, the invention can be practiced otherwise than has beenspecifically shown and described.

What is claimed is:
 1. A method of protecting glass sheets fromscratching comprising applying a discontinuous layer of slip agent to asurface of a glass sheet before a finishing operation, wherein said slipagent is applied to said glass sheet by transferring said slip agentfrom a carrier membrane including said slip agent, removing said carrierbefore said finishing operation, said slip agent comprising a long chainfatty ester or long chain fatty amide, and inhibiting scratching of saidglass sheet during said finishing operation using said discontinuouslayer of slip agent.
 2. The method of claim 1 wherein said applicationof said slip agent to said surface of said glass sheet forms surfaceroughness on said glass sheet comprising said slip agent.
 3. The methodof claim 1 wherein said long chain fatty amide is erucamide.
 4. Themethod of claim 1, wherein said slip agent is present on said glasssheet in an amount ranging from 1 to 10,000 nanograms per centimeter².5. The method of claim 1, wherein said slip agent is present on saidglass sheet in an amount ranging from 1 to 3,000 nanograms percentimeter².
 6. The method of claim 1, wherein said slip agent ispresent on said glass sheet in an amount ranging from 1 to 500 nanogramsper centimeter².
 7. The method of claim 1, wherein the carrier membraneis a paper or film.
 8. The method of claim 7, wherein said slip agent isapplied to said glass sheet using a process selected from the groupconsisting of a pressure wall process, a laminated film process, and astacked glass with interleaf compression process.
 9. The method of claim8, comprising the steps of: a) positioning said paper or film on one ofsaid glass sheets such that said slip agent included on said paper orfilm is in contact with said glass sheet; b) pressing said paper or filmagainst said glass sheet; c) transferring at least a portion of saidslip agent from the paper or film onto said glass sheet; and d) removingsaid paper or film from said glass sheet, while leaving said slip agenton the glass sheet.
 10. The method of claim 9 further comprising thesteps of: e) placing an additional said glass sheet against an interleafpaper including said slip agent such that said slip agent is presentedon said interleaf paper is in contact with said additional said glasssheet; f) repeating said steps a) and e) until a stack of said glasssheets is arranged with said interleaf paper between adjacent said glasssheets; g) wherein said steps b) and c) occur when said interleaf paperlocated between said glass sheets is compressed as a result of a weightof said stack; and h) resisting scratching from glass or other particleson the glass sheets when the glass sheets move relative each other withthe interleaf paper.